In an image forming apparatus, such as a copier, that performs image formation by developing, with toner, an electrostatic latent image that has been formed on a photoconductor to form a toner image and by transferring the toner image onto paper serving as a recording medium, the surface potential of the photoconductor in the main-scanning direction may become uneven because of variations in distance between a corona charger and the photoconductor in the main-scanning direction of the photoconductor (a tilt of the corona charger). Consequently, for example, fog of toner may appear at a portion of the photoconductor in the main-scanning direction.
Conventionally, in order to resolve the problem described above, an analog image forming apparatus is caused to copy a white reference original, and an adjustment toner image is formed on a recording medium on the basis of an electrostatic latent image formed through radiation based on an image of the original performed at that time according to PTL 1, for example. PTL 1 also discloses that a tilt of a corona charger relative to a photoconductor is adjusted on the basis of a density of this adjustment toner image.
However, PTL 1 describes an analog development (normal development) method, and thus the adjustment toner image is formed in a region corresponding to an exposed portion which is a bright portion exposed to light by an exposure means.
Thus, the density of the toner image on the recording medium varies due to the influence of variations in an amount of exposure given by the exposure means. If the amount of exposure given by the exposure means is uneven, it is difficult to accurately measure an amount of variations in density caused by a tilt of the corona charger, and consequently highly accurate tilt adjustment cannot be performed.
PTL 2 has proposed a technique for forming an adjustment toner image used to adjust a tilt of a corona charger by attaching toner onto a dark portion potential on the surface of a photoconductor without performing exposure by an exposure means, in order to suppress a decrease in accuracy in adjustment of a tilt of the corona charger due to variations in an amount of exposure given by the exposure means in an image forming apparatus that adjusts a tilt of the corona charger by using a toner image output on a recording medium.